1. Field of the Invention
The present invention relates to an optical transmittance adjusting device for use in a display apparatus such as a liquid crystal TV, an imaging apparatus such as a video camera, a copying apparatus, and an optical apparatus such as a camera, and in particular to an optical transmittance adjusting device for adjusting a contrast ratio of an image obtained by the above-mentioned apparatuses and partially controlling an amount of light incident on the apparatuses.
2. Description of the Related Art
Conventionally, the contrast ratio of an image is adjusted mainly by the following methods.
(1) Covering an original image with a filter
This method is used in a copying apparatus or the like for copying an image having a half tone area such as a photograph. Usually, the original image is covered with a filter such as a silk screen for decreasing the contrast ratio.
(2) Covering an illuminating lamp with a filter
A surface of a flash lamp or an illuminating lamp is covered with a filter, thereby uniformizing an intensity of the illuminating light for decreasing the contrast ratio of the image.
(3) Using an image processing technology
Using a technology for detecting an edge of an image or other technologies, the contrast ratio of the image is electrically increased or decreased.
Backlight compensation, which is an example of partially adjusting an amount of incident light, will be described in the case of a camera and a video camera.
In a camera, an operator manually pushes a backlight compensation button when judging that backlight is incident. When the button is pushed, exposure is increased to above a level set by an automatic exposure adjusting device, thereby preventing an image of an object to be shot from being darkened.
In an imaging apparatus using a CCD (charge coupled device), such as a video camera, an image read by the CCD is divided into six areas, and data for each area is processed in accordance with a specified priority order for automatic backlight compensation. Practically, when the backlight is incident on an area having a high priority, all the six areas are darkened to adjust an image of an object to be shot; and when the backlight is incident on an area having a low priority, no contrast ratio adjustment is conducted.
As is apparent from the above description, the contrast ratio is conventionally adjusted for an image of an object before the object is shot. For an obtained image, only image processing is performed. The use of an image processing technology requires a high performance computer and data processing software, and a high level of skill for operating the computer and software. Accordingly, it is difficult for laymen to operate the conventional optical transmission adjusting devices.
For backlight compensation in a camera, an operator manually pushes the button when judging that backlight is incident. Accordingly, whether proper compensation is performed or not depends on skill and experience of the operator, which restricts accurate compensation. Further, the compensation can be performed by a uniform extent, but cannot be performed in accordance with the amount of incident light. In backlight compensation in an imaging apparatus such as a video camera, when backlight is incident on an area having a high priority, there is an undesirable possibility that the image is entirely darkened. In contrast, when backlight is incident on an area having a low priority, no contrast ratio adjustment is conducted, thereby making the image too bright in that area. In either case, the quality of the image is low.